Lubricous coating for glass containing polyvinyl alcohol, emulsified polyethylene andan inorganic acid



United States Patent 3,357,853 LUBRICOUS COATING FOR GLASS CONTAININGPOLYVINYL ALCOHOL, EMULSIFIED POLYETH- YLENE AND AN INORGANIC ACID JohnE. Pickard, Selma, Ind., assignor to Ball Brothers Company Incorporated,Muncie, Ind., a corporation of Indiana No Drawing. Filed Jan. 2, 1964,Ser. No. 335,390 21 Claims. (Cl. 117-124) ABSTRACT OF THE DISCLOSURE Aglass coating composition including polyvinyl alcohol, emulsifiedpolyolefin and an inorganic acid, a method of coating a glass surfaceinvolving applying said coating composition to a glass surface andheating to a temperature of at least about 160 F., and glass articles socoated.

The present invention relates to a new and improved durable, lubricouscoating for glass and more particularly relates to an improved lubricouscoating for glass articles such as glassware, to a novel method offorming such a coating on glass, and to a new composition employed inthe formation of such a coating.

Glass articles such as glasware, are handled a great number of timesduring manufacture, inspection, shipping, filling, use, etc. During suchhandling, the Ware comes into contact withvarious mechanical devicessuch as feeders, conveyors, inspection devices and the like and alsocontacts other pieces of ware and surfaces such as boxes, shelves, etc.

This high degree of contact causes damage either by breakage, cracking,scratching or other defacing of the surface thereof. Breakage duringprocessing creates a serious problem in that a processing line may jamwhich requires attention by a person, e.g., to clean the broken Warefrom the line. The possibility of interruption of a line due to breakageof ware necessitates a higher degree of supervision than may actually berequired. Breakage during procesing is also serious because of thepossibiliity of slivers or fragments of the shattered glass beingdeposited in adjacent Ware which is undesirable in most situations andis completely unacceptable when the ware is to be used for foodpackaging. Attempts have been made in the past to minimize or eliminatethe above difficulties by the application of various coatings to glass.While the coatings proposed, in some cases, have reduced breakage anddamage to some degree, the coatings have created other problems. In somecases it has been difiicult to apply the coating composition to the wareand/ or labels did not tightly adhere to the coated surfaces. Othercoatings did not retain lubricity after washing or steam cleaning andthus were unsuccessful. Many coatings were not acceptable becausetheyhad not been approved for use in food. Thus, none of the coatingsproposed provided the desired combination of improved properties.

In view of the above and other difliculties and problems with coatingsfor glass heretofore employed, it was completely unexpected andsurprising to discover a new and improved coating for glass whichovercomes many of the problems encountered in the past and, in addition,provides benefits and advantages heretofore unattainable. The coating ofthe present invention provides a highly lubricous surface on glass whichreduces damage during handling to a minimum. Also, the coating isdurable and does not lose its effectiveness when cleaned with hot wateror steam. Furthermore, the coating provides a surface to which labelsadhere tightly even after extended periods of storage and handling.Moreover, the method of coating glass surfaces in accordance with theinvention is simple and convenient and relatively low in cost. Anotheradvantage of the coating of the invention is that the appearance of theglass is not changed.

The novel lubricous coating for glass of the present invention comprisesa reaction product of polyvinyl alcohol, an emulsified polyolefin and aninorganic acid. The coating of the present invention is advantageouslyformed on glass by applying a mixture of polyvinyl alcohol, anemulsified polyolefin and an inorganic acid to the glass and heating thecoating to an elevated temperature. During heating, the components ofthe coating composition react to produce a durable, lubricous,substantially waterinsoluble coating.

The polyvinyl alcohol advantageously is a substantially completelyhydrolyzed polymer, that is, a polymer with less than about 5% by weightof residual acetate groups and a saponification number of less thanabout 40. Preferably, the polyvinyl alcohol has less than about 1%residual acetate groups and a saponification number of less than about20.

The polyolefin employed in the coating of the present inventionadvantageously has a molecular weight of less than about 3000 andpreferably in the range of about 1200 and 2700. Preferably, thepolyolefin is a polyethylene having a molecular weight in the range ofabout 1600 to 2500.

The inorganic acid employed in the coating of the invention may be anacid such as phosphoric acid, chromic acid, hydrochloric acid, and thelike. Advantageously, the acid is a relatively strong mineral acid andpreferable is concentrated phosphoric acid.

In addition to the principal components of the coating as set forthabove, other materials may be included therein provided they do notdeleteriously affect the improved properties and characteristics of thecoating. For example, a pigment may be incorporated in the coatingcomposition and dispersing or emulsifying agents may be employed tofacilitate mixing of the components of the coating composition. Inaddition, it maybe desirable to improve the shelf life of thecomposition by incorporating stabilizers, bactericides, mold inhibitorsor similar materials.

The proportions of the polyvinyl alcohol, the polyolefin, and theinorganic acid in the coating and in the coating composition of theinvention are generally about equal. Advantageously, the proportion ofthe polyolefin is slightly less than that of the polyvinyl alcohol, forexample, about 40% to 90% by weight of the polyvinyl alcohol. Theproportion of the inorganic acid advantageously is somewhat greater thanthat of the polyvinyl alcohol, for example, about to 300% by weight ofthe polyvinyl alcohol.

The coating composition of the present invention may be prepared byforming an emulsion of the polyolefin, part of the polyvinyl alcohol andan emulsifying agent in Water. After the emulsion is formed, theremainder of the polyvinyl alcohol is incorporated into the emulsion.Generally, a concentrate is prepared and then diluted as required. Theconcentrate is diluted with water and the inorganic acid to provide aconcentration of polyvinyl alcohol in the final coating composition ofbetween about 0.001% and 5% and preferably between about 0.05% and 0.2%by weight of the composition. Although compositions containingproportions of polyvinyl alcohol outside the preferred range producebenefits and advantages of the invention, the lower concentrations tendto produce very thin coatings which are less desirable since a number ofcoats are required, while higher concentrations tend to producecompositions of higher viscosity which make it more difficult to form asmooth, uniform coating.

The composition of the present invention employed to coat the glassadvantageously comprises between about 0.001% and 5% by weight ofpolyvinyl alcohol, and preferably between about 0.05% and 0.2% as setforth above. The concentration of the polyolefin is advantageouslybetween about 0.001% and 5% by weight of the composition and preferablybetween about 0.04% and 0.15%. Advantageously, the inorganic acidcomprises between about 0.001% and 6% by weight of the composition witha concentration in the range of about 0.06% and 0. 25% being preferred.

The composition may be applied to the glass by any convenient method andpreferably by spraying or atomizing. Advantageously, the composition isapplied to the glass at a temperature above about 160 F. Coating of theglass may be conveniently accomplished as the glass emerges from anannealing lehr. However, if desired, the composition may be applied tocold glass either before or during reheating thereof.

The maximum temperature to which the coating is exposed to form thedesired reaction product is not critical but is limited only by thetemperature which causes the glass to thermo-check, that is, cracking orcrazing of the surface. Preferably, the coating is heated to atemperature in the range of about 180 to 500 F.

The invention will be described in detail with reference to thefollowing examples. It is intended that the examples be illustrative ofthe invention and not limiting the invention to the specific proceduresand conditions set forth. In the examples, parts and percentages are byweight.

Example I Eight parts of polyethylene having a molecular weight of about2500 which had been previously melted, were mixed with about 1 part ofpolyvinyl alcohol containing less than about 1% of residual acetategroups and having a saponification number less than about 12, 2 parts byweight of polyoxyethylene sorbitan monostearate and 20 parts of boilingwater. The mixture was agitated thoroughly and then added to about 11parts of the above polyvinyl alcohol which had been dissolved in about200 parts of hot water. Ten parts of the above mixture were then dilutedwith about 590 parts of water and 0.7 part of concentrated phosphoricacid (85% The resulting composition containing about 0.08% polyvinylalcohol, 0.07% polyethylene, and 0.1% phosphoric acid was sprayed onto aseries of S-ounce glass baby food jars as the jars emerged from anannealing lehr. The jars were at a temperature of about 200 F. Thecoated jars were allowed to cool slowly while maintaining a temperatureabove about 160 F. for about 1 minute.

Samples of the coated jars, together with uncoated control samplesformed prior to and succeeding the coated jars, were tested to determinethe coelficient of friction of the external surface thereof. Thecoefiicient of friction for the coated jars was only about one-fourththat of the similar uncoated jars.

The durability of the coating was determined by submerging the jars in apressure cooker. The water in the cooker was heated to about 250 F. andmaintained at about 15 p.s.i. pressure for approximately 30 minutes. Thejars were removed from the pressure cooker and permitted to cool and thelubricity checked again. Although the coefficient of friction for thecoated jars was slightly greater, it Was still only about one-third thatof similar uncoated jars.

Labeling tests were also conducted with samples of the coated jars todetermine the labeling characteristics. In all cases, labels adheredtightly even after exposing the labeled jars to a steam treatment atabout 220 F.

Example II The procedure of this example was the same as that of Example1, except that about 4 parts of polyethylene were employed in place ofthe quantity recited in Example I. After dilution, the compositionapplied to the jars contained about 0.08% polyvinyl alcohol, 0.035%polyethylene and 0.1% phosphoric acid.

The coated jars were tested according to the procedures of Example I andfound to show the improvements and advantages exhibited by the coatedjars of Example I.

Example III The procedure of this example was the same as that ofExample 1, except that about 0.4 part of phosphoric acid was employed indiluting the concentrated mixture to form the coating composition.

The coating was applied to glass jars by spraying while the jars were ata temperature of approximately 180 F. The coated jars were tested andfound to show improvements over uncoated jars similar to those ofExamples I and II.

Example IV The procedure of this example was the same as that of ExampleI, except that 0.6 part of chromic acid was used instead of thephosphoric acid. Coated jars exhibited the superiorities and advantagesshown by the coated jars of Exampels I, II, and III.

It is clear from the above description and examples that the presentinvention provides a new and improved coating for glass which overcomesmany of the problems encountered heretofore and in addition, providesbenefits and advantages which previously were not attainable. Thecoating of the invention provides a highly lubricous, durable coatingwhich greatly minimizes damage to glass during handling and use.Moreover, labels adhere tightly to the coated surfaces even afterextended periods of handling and storage. In addition, the method of theinvention for coating glass surfaces is simple and convenient andrelatively low in cost. Furthermore, the coating of the invention doesnot change the appearance of the glass.

It will be apparent from the above description that variousmodifications in the formulations and procedures described may be madewithin the scope of the invention. Therefore, the invention is notintended to be limited to the specific details described herein exceptas may be required by the following claims.

What is claimed is:

1. A glass article coated with a durable, lubricous coating comprisingthe reaction product of polyvinyl alcohol having less than about 5% byweight of residual acetate groups, an aqueous emulsion of polyethylenehaving a molecular weight less than about 3,000, and an inorganic acid,said polyethylene being present as a reactant in amounts between about40% and 90% by weight of the amount of polyvinyl alcohol present as areactant, and said acid being present as a reactant in amounts betweenabout and 300% by weight of the amount of polyvinyl alcohol in saidcoating.

2. An article as claimed in claim 1 wherein said polyvinyl alcohol hasless than about 1% by weight of residual acetate groups.

3. An article as claimed in claim 1 wherein said polyethylene has amolecular weight between about 1,200 and 2,700.

4. An article as claimed in claim 1 wherein said inorganic acids areselected from the group consisting of phosphoric acid, chromic acid, andhydrochloric acid.

5. A glass article coated with a durable lubricous coating comprisingthe reaction product of polyvinyl alcohol having less than about 1% byweight of residual acetate groups, an aqueous emulsion of polyethylenehaving a molecular weight between about 1,600 and 2,500, and aninorganic acid, said polyethylene being present as a reactant in amountsbetween about 40% and by weight of the amount of polyvinyl alcoholpresent as a reactant, and said acid being present as a reactant inamounts between about 80% and 300% by weight of the amount of polyvinylalcohol in said coating.

6. A method of forming a durable, lubricous coating on a glass surfacewhich comprises applying to said surface an aqueous mixture comprisingbetween about 0.001% and 5% by weight of polyvinyl alcohol having lessthan 5% residual acetate groups, between about 0.001% and 5% by weightof emulsified polyethylene having a molecular weight of less than about3,000, and between about 0.001% and 6% by weight of an inorganic acid,and heating said mixture to a temperature of at least 160 'F., wherebysaid mixture forms a durable, lubricous coatng on said glass surface.

7. A method as claimed in claim 6 wherein said po1y vinyl alcohol hasless than 1% by weight residual acetate groups.

8. A method as claimed in claim 6 wherein said polyvinyl alcohol ispresent in said aqueous mixture in amounts between about 0.005% and 0.2%by weight.

9. A method as claimed in claim 6 wherein said polyethylene has amolecular weight between about 1,200 and 2,700 and is present in saidaqueous mixture in amounts between about 0.04% and 0.15% by weight.

10. A method as claimed in claim 6 wherein said inorganic acid isselected from the group consisting of phosphoric acid, chromic acid, andhydrochloric acid.

11. A method as claimed in claim 6 wherein said mixture is heated to atemperature between about 180 F. and 500 F.

12. A method of forming a durable, lubricous coating on a glass surfacewhich comprises applying to said glass surface an aqueous mixturecomprising between about 0.05 and 2% by weight of polyvinyl alcoholhaving less than 1% residual acetate groups, between about 0.04% and0.15% by weight of emulsified polyethylene having a molecular weightbetwen about 1,600 and 2,500, and between about 0.06% and 0.25% byweight of an inorganic acid, and heating said mixture to a temperatureof at least about 160 F.

13. A coating composition for forming durable, lubricous coatings onglass surfaces comprising as an aqueous mixture, between about 0.001%and 5% by weight of polyvinyl alcohol having less than 5% residualacetate groups, between about 0.001% and 5% by weight of emulsifiedpolyethylene having an average molecular weight less than 3,000, andbetween about 0.001% and 6% by weight of an inorganic acid.

14. A coating composition as claimed in claim 13 wherein said polyvinylalcohol has less than 1% residual acetate groups.

15. A coating composition as claimed in claim 13 wherein said polyvinylalcohol is present in amounts between about 0.05 and 0.2% by weight.

16. A coating composition as claimed in claim 13 wherein saidpolyethylene has a molecular Weight between about 1,200 and 2,700.

17. A coating composition as claimed in claim 13 wherein saidpolyethylene is present in amounts between about 0.04% and 0.15 byweight.

18. A coating composition as claimed in claim 13 wherein said inorganicacid is present in amounts between about 0.06% and 0.25%.

19. A coating composition for forming durable, lubricous coatings onglass surfaces comprising, as an aqueous mixture, between about 0.05%and 0.2% by weight of polyvinyl alcohol having less than 1% residualacetate groups, between about 0.04% and 0.15% by weight of emulsifiedpolyethylene having an average molecular weight between about 1,600 and2,500, and between about 0.06% and 0.25 by weight of an inorganic acid.

20. A coating composition as set forth in claim 19 wherein saidinorganic acid is selected from the group consisting of phosphoric acid,chromic acid, and hydrochloric acid.

21. A coating composition for forming durable, lubricous coatings onglass comprising, as an aqueous mixture, between about 0.01% and 5% byweight of polyvinyl alcohol having less than 5% residual groups, betweenabout 0.01% and 5% by weight of emulsified polyethylene having amolecular weight less than 3,000, and between about 0.001% and 6% byweight of phosphoric acid.

References Cited UNITED STATES PATENTS 2,948,697 8/ 1960 Robertson26029.6 2,995,533 8/1961 Parmer et al 117-124 X 3,157,611 11/1964Lindemann 26029.6

ALFRED L. LEAVITT, Primary Examiner.

H. COHEN, Assistant Examiner.

1. A GLASS ARTICLE COATED WITH A DURABLE, LUBRICOUS COATING COMPRISINGTHE REACTION PRODUCT OF POLYVINYL ALCOHOL HAVING LESS THAN ABOUT 5% BYWEIGHT OF RESIDUAL ACETATE GROUPS, AN AQUEOUS EMULSION OF POLYETHYLENEHAVING A MOLECULAR WEIGHT LESS THAN ABOUT 3,000, AND AN INORGANIC ACID,SAID POLYETHYLENE BEING PRESENT AS A REACTANT IN AMOUNTS BETWEEN ABOUT40% AND 90% BY WEIGHT OF THE AMOUNT OF POLYVINYL ALCOHOL PRESENT AS AREACTANT, AND SAID ACID BEING PRESENT AS A REACTANT IN AMOUNTS BETWEENABOUT 80% AND 300% BY WEIGHT OF THE AMOUNT OF POLYVINYL ALCOHOL IN SAIDCOATING.